As a composite material, unsaturated polyester resin has been well applied in the fields of coatings, glass reinforced plastics, artificial stone, and handicrafts. However, the yellowing of the color of the unsaturated resin has always been a problem that plagues the manufacturer. Generally, the yellowing causes of unsaturated resins include the following: during the esterification synthesis of unsaturated resins, the yellowing of heat aging due to high temperature, the esterification temperature of unsaturated resins is generally 180-220 ° C or higher, here At room temperature, the resin is easily yellowed due to heat aging, affecting the appearance of the resin product; the yellowing caused by the contact of the resin with ultraviolet rays is mainly caused by the presence of a benzene ring in the resin (including aromatic dibasic acid/anhydride and styrene introduced by styrene). Ring), the reason may be that the aromatic compound undergoes thermal oxygen degradation at high temperature, and the electronic transition in the π→π orbital is easy to occur, so that the resin appears yellow; in the resin production process, the raw material is exposed to oxygen due to poor sealing of the device and the like. The general unsaturated polyester molecular chain contains not only ester groups, hydroxyl groups, carboxyl groups, but also double bonds and aromatic rings. A trace amount of oxygen can cause thermal oxidative degradation, and the obvious performance is that the resin color turns yellow. The effects of additives such as antioxidants, polymerization inhibitors, curing agents, etc., amine antioxidants are easily converted into nitroxide radicals to color the product, commonly used polymerization inhibitors, such as hydroquinone, in the presence of trace oxygen Oxidation to oximes, bismuth itself has a color, which affects the color of the resin. Some manufacturers still use a peroxide acyl-tertiary amine system and a ketone-metal soap system, due to both tertiary amines and metal soaps. The color is easy to color the resin.
Of course, there are other reasons why the resin turns yellow. In general, hot oxygen and ultraviolet light are the main causes of yellowing. The use of a saturated dibasic acid (or anhydride) in place of an aromatic dibasic acid (or anhydride), although the color of the resin can be somewhat lighter, but this method is not sufficient considering various factors such as resin properties and cost. ideal. In addition to the inert gas in the production and storage process as much as possible to isolate the contact with oxygen, a more effective method is to add antioxidants and UV absorbers, which can effectively prevent yellowing of the delayed polyester. The anti-yellowing solution recommended by experts is anti-yellowing solution: the use of amine-free antioxidants, but the use of primary and secondary antioxidants, the main antioxidants are usually hindered phenols, can capture peroxide free radicals The auxiliary antioxidant is a phosphite, which can decompose the metal peroxide while decomposing the hydroperoxide to prevent oxidative discoloration of the resin. If you want to further improve the resistance to yellowing and weathering, it is recommended to add UV absorbers. Adding UV absorbers can effectively inhibit the yellowing of polymer materials under UV light and provide excellent protection for products. The reduction of gloss, cracks, bubbles, delamination, significantly improve the weatherability of the product, and has a good synergistic effect with the use of antioxidants. Of course, the use of antioxidants and UV absorbers can not fundamentally solve the yellowing problem, but within a certain range, it can effectively prevent the oxidation of yellowing of unsaturated polyester products, keep the product color transparent, and improve the product. Grade.